Neptune's wild days: constraints from the eccentricity distribution of the classical Kuiper Belt

TL;DR

This study constrains Neptune's past orbital behavior by analyzing the eccentricity distribution of Kuiper Belt objects, revealing that moderate eccentricity with specific migration patterns best explains the observed populations.

Contribution

It introduces a comprehensive model that constrains Neptune's eccentricity and migration parameters based on Kuiper Belt object distributions, improving understanding of the planet's dynamical history.

Findings

Moderate Neptune eccentricity (e > 0.15) with 1-6 AU migration best fits observations.

Cold KBOs are confined to low eccentricities, constraining Neptune's past orbit.

Interactions with Uranus influence the dynamical excitation of cold KBOs.

Abstract

Neptune's dynamical history shaped the current orbits of Kuiper belt objects (KBOs), leaving clues to the planet's orbital evolution. In the "classical" region, a population of dynamically "hot" high-inclination KBOs overlies a flat "cold" population with distinct physical properties. Simulations of qualitatively different histories for Neptune -including smooth migration on a circular orbit or scattering by other planets to a high eccentricity - have not simultaneously produced both populations. We explore a general Kuiper belt assembly model that forms hot classical KBOs interior to Neptune and delivers them to the classical region, where the cold population forms in situ. First, we present evidence that the cold population is confined to eccentricities well below the limit dictated by long-term survival. Therefore Neptune must deliver hot KBOs into the long-term survival region without excessively exciting the eccentricities of the cold population. Imposing this constraint, we explore the parameter space of Neptune's eccentricity and eccentricity damping, migration, and apsidal precession. We rule out much of parameter space, except where Neptune is scattered to a moderately eccentric orbit (e > 0.15) and subsequently migrates a distance Delta aN=1-6 AU. Neptune's moderate eccentricity must either damp quickly or be accompanied by fast apsidal precession. We find that Neptune's high eccentricity alone does not generate a chaotic sea in the classical region. Chaos can result from Neptune's interactions with Uranus, exciting the cold KBOs and placing additional constraints. Finally, we discuss how to interpret our constraints in the context of the full, complex dynamical history of the solar system.